Anti-CD20 monoclonal antibodies (mAbs) such as rituximab have become a cornerstone in the therapy of B cell non-Hodgkin lymphomas (NHL), but are only partially effective, as most patients eventually relapse and remain incurable. While current genetic engineering and efforts are yielding mAbs with enhanced antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC) and pro-apoptotic functions, these improvements are largely incremental, and do not result in mAbs capable of altering the tumor microenvironment and adjacent host immune cells to favor immune- mediated tumor destruction. We hypothesize that the efficacy of anti-lymphoma mAbs can be improved by linking these precise tumor-targeting vehicles to immunomodulatory substances for release within the tumor microenvironment. Our laboratory has now collected a unique set of cell line models and anti-CD20 reagents including murine lymphomas expressing human CD20, human CD20 transgenic mice, and anti-murine CD20 mAbs that for the first time allow detailed modeling of anti-CD20 therapy in immunocompetent hosts. Toll-like receptor 9 (TLR9) agonist CpG oligodeoxynucleotides are prime candidates for boosting anti-lymphoma immunity, as direct intratumoral injection shows promising anti- tumor effects in both animal and clinical studies. In order to target CpG to all tumor sites in vivo, we adopted an antibody conjugation technique we recently described to achieve direct chemical linkage of CpG to the anti-CD20 antibody rituximab. Remarkably, the antibody-CpG conjugate was able to reproducibly eradicate established tumors from 100% of mice bearing a highly aggressive, rituximab- resistant human CD20+ B cell lymphoma. We thus propose the following aims to characterize the activity, mechanisms of action, and clinically-relevant translational principles for antibody-CpG conjugates against B cell lymphomas: Aim 1. Evaluate the efficacy of novel rituximab-CpG conjugates in syngeneic, immunocompetent mice bearing 2 different murine lymphomas expressing human CD20. Aim 2. Compare the in vivo efficacy of rituximab conjugates containing CpG oligodeoxynucleotides of the functionally distinct A, B, and C classes. Aim 3. Determine the mechanisms of anti-tumor action for rituximab-CpG in syngeneic models, and whether tumor regression leads to secondary adaptive T cell responses against tumor antigens released from dying lymphoma cells. Aim 4. Test rituximab-CpG conjugates against human B cell lymphoma xenografts and primary human lymphoma specimens grown in immunodeficient mice. Aim 5. Explore antibody-CpG conjugates targeting alternative B cell lymphoma surface antigens such as CD19, that internalize upon antibody binding, further broadening the applicability of this approach.